1. Field of the Invention
The present invention relates to an ultrasound observation system that generates an image based on an ultrasound signal that is obtained by transmitting and receiving ultrasound, and also to an operation method of the ultrasound observation system.
2. Description of the Related Art
Ultrasound diagnostic apparatuses that have an ultrasound endoscope and are equipped with an elastography function that displays the elasticity of tissue are in practical use. Such ultrasound diagnostic apparatuses are configured to generate an elasticity image (elastography mode image) that represents the rigidity or softness of living tissue based on the amount of strain in the living tissue that is generated by a pressing force.
An elasticity modulus for generating an elasticity image is determined based on a displacement amount of living tissue that is produced as a result of a surgeon pressing a probe against the living body or based on a displacement amount of living tissue that arises due to beating (pulsation).
On the other hand, in the case of displaying elasticity images utilizing an ultrasound endoscope, it is conceivable to utilize a displacement caused by beating (pulsation).
For example, in Japanese Patent Application Laid-Open Publication No. 2010-82337, technology for an ultrasound observation apparatus that displays the elasticity of living tissue is disclosed that presses living tissue by inserting a fluid into a balloon and withdrawing the fluid therefrom. At such case, a pressure sensor is provided that measures the pressure inside the balloon, and pressure transitions as well as the degree of expansion and contraction of the balloon are displayed on a monitor so that an examiner can visually ascertain such information. In addition, the aforementioned publication discloses an embodiment that, in a case where an appropriate amount of pressing with respect to the living tissue of a subject cannot be obtained only by inserting and withdrawing fluid by manual operation of a lever by the examiner, supports the performance of an appropriate pressing operation by using a control adjustment portion that inserts and withdraws fluid in an auxiliary manner.
Further, Japanese Patent Application Laid-Open Publication No. 2006-230618 discloses technology for an ultrasound observation apparatus that measures properties such as the elasticity of tissue which, to enable stable measurement even in the case of tissue that periodically changes shape, such as the heart, varies the gain of an ultrasound signal in synchrony with a heartbeat cycle that is measured by an electrocardiograph or the like, and thus suppresses the occurrence of a situation in which the reception level fluctuates accompanying changes in tissue shape. Further, as another embodiment in the aforementioned publication; technology is disclosed that uses an excitation apparatus to periodically change the shape of a static organ that does not actively change shape, and measures the elasticity thereof.
In addition, International Publication No. WO 2011/034005 discloses technology that, in an ultrasound observation apparatus that displays the elasticity of tissue, extracts and displays an image of tissue in an appropriate pressed state based on displacement data, elasticity data, an electrocardiographic waveform or the like.